Quasi-moving block system of train control

ABSTRACT

A system of train control uses a quasi-moving block methodology for controlling operation of a plurality of trains from a remote office. The office parses the route information for each train into non-overlapping movement authorities that are issued via a communications network. As each train proceeds, it communicates with the office to automatically roll up its movement authority and release the portion of the movement authority behind the train. The office then extends the movement authority of the subsequent train to reflect the released portion of the movement authority of the leading train. The track can be divided into a series of track circuits to enable detection of broken rail or unexpected occupancy. The office segment can then control operation of trains accordingly if broken rail or unexpected occupancy is detected in the train&#39;s movement authority.

RELATED APPLICATION

The present application is based on and claims priority to theApplicant's U.S. Provisional Patent Application 63/125,518, entitled“Quasi-Moving Block System of Train Control,” filed on Dec. 15, 2020.

GOVERNMENT LICENSE RIGHTS

This invention was made with government support under work sponsored bythe Federal Railroad Administration of the U.S. Department ofTransportation under contract DTFR5311-D00008L. The government hascertain rights in the invention.

BACKGROUND OF THE INVENTION Field of the Invention

The present invention relates generally to the field of control systemsfor trains and other rail vehicles. Throughout this document, the term“train” is used to mean either train or rail vehicle. More specifically,the present invention discloses a system for controlling operation oftrains using a hybrid approach of fixed block and moving block traincontrol, referred to as quasi-moving block (QMB) train control whileleveraging conventional train control infrastructure and Positive TrainControl (PTC), also known as Communications-Based Train Control (CBTC)movement authority architecture.

Statement of the Problem

The most widely deployed CBTC systems in the United States arefixed-block systems, meaning that they operate based on detection of anoccupancy or rail break anywhere within their fixed block limits. Due totheir fixed-block nature, they cannot tell where within a block that arail break or occupancy has occurred. Because of this uncertainty,fixed-block CBTC systems cannot provide collision protection betweentrains operating within the same block; they only limit speed in thatcase. A fundamental objective of the present invention is to addcollision protection within the same block.

One of the conventional modern types of signaled territory for higherdensity lines is Centralized Traffic Control (CTC, also known as TrafficControl or TC). A typical CTC installation allows a dispatcher to managetraffic remotely via field interlocking systems and wayside signals.Signals in CTC territory are generally one of two types (with theexception of signals associated with automatic interlockings atdiamonds): (1) a control point (CP), which is an absolute signal that isremotely controlled by a train dispatcher in conjunction with fail-safefield logic; or (2) an intermediate (or automatic) signal that iscontrolled automatically by the conditions of the track in that signal'sblock and by the status of the signal or track circuits ahead. CPsdesignate the boundaries of control blocks and are usually located atthe extremities of sidings, junctions, crossovers between adjacenttracks, and manual diamond crossings. Code line systems are used to linkthe computer-aided dispatch (CAD) system with field interlockings. Thedispatcher requests a route, the request is sent to field interlockinglogic at CPs along the route via the code line system, and safety isverified in a fail-safe manner by the field interlocking beforeexecution and providing indication back to the CAD system.

FIG. 1 provides an illustration of CTC with single and multiple tracks.As shown, a control block spans between two CPs. Typically, multipleintermediate blocks are typically within a control block and useAutomatic Block Signaling (ABS). The ABS system typically relies ontrack circuits for track occupancy and broken rail detection.Information about the status of each block is typically transmitted toadjacent blocks through the use of coded track circuits. With codedtrack circuits, the electrical signal that is transmitted through therails is coded using different pulse rates to indicate the signal aspectthat block is currently displaying. This information is interpreted bythe equipment at the adjacent block limit and used in determining theproper aspect to display for the signal governing movement over thatblock.

In non-signaled territory, the dispatcher issues authority for aspecific train to occupy a given section of track. Track Warrant Control(TWC) is the General Code of Operating Rules (GCOR) method of traincontrol most commonly used in non-signaled territory. Other operatingrules use methods similar to TWC in non-signaled territory. While thisapplication gives examples in terms of GCOR, QMB is equally applicablewhere other rulebooks are in effect. QMB typically requires trackcircuits, and so is not fully applicable to non-signaled territoryunless track circuits are installed throughout. However, a QMB traincontrol system can operate as a full moving block (FMB) system where notrack circuits exist. It is possible to have a combination of TWC andABS (TWC-ABS), where the track warrant grants the movement authority,and the ABS system provides train separation as well as broken rail androllout (unauthorized occupancy) protection. TWC-ABS territory isamenable to conversion to QMB operation since track circuits are alreadypresent.

The Rail Safety Improvement Act of 2008 (RSIA '08) mandatesimplementation of interoperable PTC on a significant portion of raillines in the United States. PTC, as defined in the RSIA '08, is a systemdesigned to prevent train-to-train collisions, overspeed derailments,unauthorized incursions into established roadway work zones, andmovement of a train through a mainline switch in the wrong position.There are several systems that satisfy the PTC requirements. The mostpredominant of these systems is defined by the Interoperable TrainControl (ITC) standards, which were developed by the largest U.S. ClassI freight railroads. Consequently, QMB is described herein in thecontext of the ITC PTC system, but the concept is equally applicable tomost other forms of PTC or CBTC. The example conventional PTC system(ITC PTC) described herein is referred to as “Overlay PTC (O-PTC)”.

FIG. 2 illustrates the high-level architecture of the ITC PTC system.The locomotive onboard segment determines the location of the trainrelative to the track and relative to critical assets along the trackusing a GPS-based location determination system and an onboard trackdatabase. Consist (train makeup) and route information, among otherdata, are provided to the locomotive onboard segment from the PTC backoffice during initialization. Wayside Interface Units (WIUs) 25,installed at switch and signal locations along the track, periodicallybroadcast over a wireless communications network the status of theswitch(es) and/or signal(s) they are monitoring. As the train approachesthese locations, the status messages are received by the locomotiveonboard segment. Work zones, temporary speed restrictions, and otherbulletin data are provided in digital form to the locomotive onboardsegment by the PTC back office 10 over the wireless communicationsnetwork 20.

The operational data provided to the locomotive onboard segment isprocessed to determine the operational limits (movement authority andspeed restrictions) for that train. The locomotive onboard segmentregularly updates the predicted braking distance of the train, and ifthe train is predicted to be within a specified time of violating anauthority or speed limit, warns the train crew. Additionally, the systemcan invoke a penalty brake application (should the crew fail to takeappropriate action) to prevent the violation.

Solution to the Problem

In contrast to conventional fixed-block methods of train control, thepresent invention employs a quasi-moving block (QMB) methodology. Theoffice segment receives route information from the computer-aideddispatch (CAD) system and automatically parses it into smaller,non-overlapping movement authority segments when necessary to avoidoverlap with other active movement authority segments, each segmentherein referred to as a PTC exclusive authority (PTCEA). Each PTCEA ischecked to be safe (i.e., exclusive of other PTCEAs and consistent withother conditions) and then is electronically issued to a train. One ofthe new functions introduced by QMB for the onboard segment is toautomatically roll up the PTCEA, so that a portion of its authority thatis no longer needed behind the train is released. This allows a PTCEAfor a subsequent train to be extended.

The key objective of QMB is to provide as many benefits of FMB traincontrol as possible while still utilizing fixed-block track circuits forrail integrity and occupancy detection and establishing a foundationthat can easily migrate to FMB operation when integrated with a suitablealternative to track circuits for broken rail and rollout detection. Theutilization of fixed-block track circuits prevents the need to overhaulexisting track circuits. In select circumstances and when integratedwith certain advanced technologies, QMB can perform the same as FMB,particularly when the braking distance is greater than one track circuitblock length.

In contrast to conventional train control systems, the QMB approachprovides benefits in reliability, safety, and capacity as seen inTable 1. These benefits come at the cost of modifying office functions,additional functions for the onboard segment, and optional waysidemodifications. Basic QMB does not require any modifications to thewayside, although it supports the elimination of physical signals.Optional advanced QMB technologies and functionality, includingrear-of-vehicle location determination, centralized interlocking, andadvanced broken rail detection, enable further benefits.

TABLE 1 QMB Expected Benefits Category Expected Benefit Safety Collisionprotection at all speeds (including restricted speed); with highersafety integrity when using real- time rear-of-vehicle locationdetermination. Increases pull-apart (train separation) protection whenthe real-time rear-of-vehicle location determination system reportsgreater train length than estimated, in which case the pulled-apart carsare protected by a PTC Exclusive Authority (PTCEA) and alerts. Improvedloss-of-shunt protection (using PTCEAs, train location reports, andtrain length data as additional sources of occupancy determination).Uniform method of train control using PTCEAs. Train drivers (engineers)experience a moving-block style onboard user interface in any type ofunderlying train control territory. Capacity & Increased capacity beyondthat of O-PTC if track circuits Efficiency are shortened, which is morefeasible with QMB, due to no additional aspects, elimination of waysidesignals, reduced wayside logic, possible use of jointless trackcircuits, and/or possible use of ≥1,000 MGT insulated joints. Furtherincreased capacity beyond that of O-PTC when using advanced broken raildetection (e.g., track circuits with the ability to detect a rail breakwithin an occupied block), along with rear-of-vehicle locationdetermination system (RVLDS). A following train may enter an occupiedintermediate track circuit at MAS and maintain MAS per the braking curveand PTCEA MAS limit under certain conditions. The combination of QMB, aNext Generation Track Circuit (NGTC), and RVLDS provides the sameminimum train separation as full moving block when the braking distanceis greater than one block length. QMB can reduce delays caused byapproach and time locking. When a dispatcher needs to change a routealready assigned to a train and the train's braking curve indicates thetrain can safely stop before the CP or interlocking, then the route canbe changed without time penalty. Reliability- Supports removal of signalheads and some vital field logic, Maintain- such ascoded track circuits.ability QMB with centralized interlocking simplifies field logic andfacilitates diagnostics and maintenance. It can also improve overallreliability when optional functionality that allows trains to directlycommand switches, e.g., based on their PTCEAs, is implemented.

SUMMARY OF THE INVENTION

This invention provides a system of train control using a quasi-movingblock (QMB) methodology. The office segment receives route informationfor a train from a computer-aided dispatch (CAD) system andautomatically parses it into smaller, non-overlapping movementauthorities when necessary to avoid overlap with other movementauthorities. Each movement authority is referred to as a PTC exclusiveauthority (PTCEA). A PTCEA is checked to be safe (i.e., exclusive ofother PTCEAs currently in effect) and then is issued to the train over acommunications network. The onboard segment allows the train to operateas authorized by its PTCEA, and also automatically rolls up the PTCEA,so that a portion of its authority is released behind the train when nolonger needed. This allows a PTCEA for a subsequent train to beextended. In addition, the track can be divided into a series of trackcircuits to enable detection of broken rail or unexpected occupancy. Theoffice segment can then control operation of trains accordingly ifbroken rail or unexpected occupancy is detected in the train's movementauthority.

These and other advantages, features, and objects of the presentinvention will be more readily understood in view of the followingdetailed description and the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention can be more readily understood in conjunction withthe accompanying drawings, in which:

FIG. 1 is a simplified diagram illustrating Centralized Traffic Control(CTC) with single and multiple tracks.

FIG. 2 is a diagram of the high-level architecture of the ITC PTCsystem.

FIG. 3 is a simplified diagram of the QMB functional architecture.

FIG. 4 is a simplified diagram illustrating the four messages exchangedwith a leading train.

FIG. 5 is a simplified diagram illustrating the two messages exchangedwith a leading train for more efficient use of communications bandwidthin QMB operation.

FIG. 6 illustrates the safety margin 54 and the PTCEA 42 for a followingtrain.

FIG. 7 is a bounce diagram illustrating the message flow for increasingand decreasing rollup rates with RVLDS.

FIG. 8 is a diagram showing a following train 42 entering an occupiedblock 34 at the maximum authorized speed (MAS).

FIG. 9 is a simplified diagram illustrating the display of a PTCEA whenthe leading train 40 does not have RVLDS.

FIG. 10 is a simplified diagram showing the message flow for rolling upa track warrant in the current ITC PTC system.

FIG. 11 is a simplified diagram showing the two messages exchanged forrollup with the present invention.

FIGS. 12-16 are diagrams of the steps involved in providing additionalprotection for joint occupancy operation by issuing and enforcing anexclusive PTCEA to each individual QMB-equipped train, workers orequipment (TWE) within work limits.

FIG. 17 is a simplified diagram illustrating a potential loss-of-shuntscenario, where Train1 maintains an active PTCEA but fails to shunt, andthe office prevents a PTCEA extension from being granted to Train2.

FIG. 18 is a simplified diagram showing an example case for pull-apartprotection.

FIG. 19 is a simplified diagram illustrating a possible margin overlapconflict.

DETAILED DESCRIPTION OF THE INVENTION

Terminology. The following words and phrases have the following meaningsas used in the present disclosure:

Bidirectional An authorization given to a train or other rail authorityvehicle to occupy and move in both directions on a section of track. Abidirectional authority may be issued exclusively to one train or mayallow joint occupancy. These authorities require additionalconsiderations beyond routine QMB operation with unidirectionalauthorities. Braking curve A train's braking distance vs. train speed,as calculated continuously by its onboard segment. Enforcing train Atrain with fully functioning PTC onboard segment (that may or may not beQMB capable), that communicates with the PTC network and can invoke apenalty brake application when required. Field interlocking Refers tovital logic at control points and logic automatic interlockings. OfficeThe railroad-specific back-office segment associated with train controland traffic control, including the dispatching system, conventional PTCBOS and other servers. PTC Exclusive An authorization given to a trainor other rail Authority (PTCEA) vehicle to occupy a section of track. APTCEA may span the entire extent of track requested by the dispatcher ormay only span an increment if the QMB office functions cannot assurethere are no conflicts beyond that increment. In QMB, all PTCEAs areexclusive (non-overlapping), except for the basic case of jointbidirectional authorities. PTCEA extension A process in which authorityis added to the current PTCEA, allowing the train to proceed farther.PTCEA rollup A process in which a train clears a portion of authorizedtrack, which is then released from the current PTCEA. Wayside logicRefers to all vital signaling logic in the field (e.g., at intermediatesignals, control points and interlockings).

The following acronyms and abbreviations have the following meanings asused in the present disclosure:

Acronym Definition ABS Automatic block signaling ATP Authority to passsignal at Stop BOS Back office server BPP Brake pipe pressure CADComputer-aided dispatch CAD-MA CAD movement authority CBTCCommunications-Based Train Control CIXL Centralized interlocking CPControl point CRC Cyclic redundancy check CTC Centralized trafficcontrol EMT Enter main track EOT End-of-train FMB Full moving block GCORGeneral Code of Operating Rules GPS Global Positioning System HMAC Hashmessage authentication code HOT Head-of-train ITC Interoperable TrainControl MAS Maximum authorized speed MD Mandatory directive NENCNon-enforcing or non-communicating NGTC Next generation track circuitO-PTC Overlay PTC PTC Positive Train Control PTCEA PTC ExclusiveAuthority QMB Quasi-moving block RSIA ′08 Rail Safety Improvement Act of2008 RSR Restricted speed restriction RURMA Rollup rate managementalgorithm RVLDS Rear-of-vehicle location determination system TBC To beconfigured TWE Train, workers, or equipment TWC Track warrant controlVBTC Virtual block track circuit WIU Wayside Interface Unit WSM WaysideStatus Message WSRS Wayside Status Relay Service

The present QMB system of train control is based on the following coreprinciples. First, train authority is granted by exclusive PTCEAs (i.e.,non-overlapping and electronically-delivered movement authorities).Every train or other rail vehicle on controlled mainline track must havea PTCEA, with the possible exception of work gangs and equipmentoperating under GCOR Track Bulletin Form B. Control of PTCEAs iscentralized in the office, which includes responsibility for issuing andextending PTCEAs. Onboard systems in each train are responsible forautomatically initiating rollup 50 of their own PTCEAs. (Note: Infailure scenarios, the crew will verbally communicate with thedispatcher.) Wayside signals are not necessary and can be removed (atleast at intermediate locations) as part of a migration/implementationplan, if not previously done. Many vital functions currently implementedin a distributed manner with field equipment may be centralized,allowing for life-cycle cost savings.

The QMB system of train control inherits principles from Overlay PTC,including: (a) WIU-to-locomotive peer-to-peer communication of waysidestatus (whether relayed by WSRS or not); (b) O-PTC onboard segmentsstates and failure processes; (c) enforcement of authority limits (e.g.,from mandatory directives); and (d) Onboard segment determines andenforces speed limit, based on the most restrictive of CAD-MA (PTCEA)speed limit, train-specific speed restriction (where applicable), andtrack speed restrictions (permanent and temporary). The QMB system alsoincludes communications features, such as providing: (a) message-basedcommunications with a retransmission protocol; (b) data integrity (e.g.,32-bit CRC or HMAC) for safety-critical messages; and (c) failedcommunications handling: (for Wayside communications, an unknown statusresults in enforcement of most restrictive state; and for officecommunications, a non-communicating indication or non-sync results increw acknowledgment and onboard segment to disengage); and (d) protocolsfor discarding redundant messages. Finally, the QMB system includes: (a)a process for providing/updating consist length data to the traincontrol system, occurring at initialization and during set-out/pick-upaccording to the railroad; (b) head-of-train (HOT) locationdetermination, utilizing today's PTC onboard location determinationsystem or more advanced solutions (e.g., including inertial sensors andadvanced algorithms); and (c) security features such as messageauthentication.

QMB inherits most of the existing overlay ITC PTC architecture. However,the same basic concept and principles can be implemented without anyrelationship to ITC PTC. FIG. 3 illustrates an example of the overallQMB architecture. The onboard segment retains all the existing corefunctionality of the Overlay PTC system. The onboard segment alsocontinues to obtain the status of field devices from Wayside StatusMessages (WSMs) generated by WIUs 25. The BOS 16 continues to be theinterface between the office 10 and the field. Minimal changes areexpected to existing CAD systems and functions.

Train movement authorities typically originate in the CAD system 12 andcan overlap. The QMB office functionality 14 parses overlapping CADmovement authorities (CAD-MAs) into exclusive PTCEAs 40, 42. PTCEAsprovide the authority for track occupancy and train movements. Theonboard segment determines speed and authority limit targets, based onthe most restrictive of PTCEAs, WSMs, train-specific speed restriction(where applicable), and permanent and temporary track speedrestrictions. CAD-MAs and PTCEAs can be issued without waiting forresponse from the interlocking system to confirm alignment of the route.This is possible because trains are also enforced by WIU indications inthe field which prevent train movement through a misaligned route.

The onboard segment includes new functions for QMB operation. One of thenew functions is for a QMB train to automatically roll up its ownunidirectional PTCEA 40, 42. This function involves determining theend-of-train (EOT) location, along with sufficient safety margin 54,either with or without a functioning rear-of-vehicle locationdetermination system (RVLDS).

QMB introduces a new set of functions for the office 14 as well, whichare responsible for the management of all PTCEAs in the system. Ittracks which PTCEAs have been issued, which PTCEA rollups/extensionshave occurred, which segments of track 30 are reserved for trains, andwhich segments of track 30 are available for use. Some interlockingfunctions that are currently implemented in the field can optionallymigrate to the office in a concept referred to as centralizedinterlocking (CIXL). QMB interfaces with either the field interlockingor CIXL if deployed. It should be understood that the office 14 can beimplemented either a remote central office or a distribute plurality ofsites.

To the extent that is practicable, QMB can use the messages that areexchanged among existing systems (PTC, CAD, and field interlocking) toimplement the communications required for the QMB interfaces with theexisting systems. If and when an interlocking becomes centralized(CIXL), a “vital” protocol will be used to assure the integrity ofmessages that remotely control the switches, similar to the protocol useto communicate safety-critical messages among PTC segments today. As theCAD system and field interlocking interfaces may not be standardized andmay depend on each railroad's implementation, the details of associatedmessage types, formats, and protocols will be defined on a case-by-casebasis.

For the interface between the QMB office functions and the onboardsegment, existing ITC messages already defined for overlay ITC PTC canbe used to the extent practicable. Messages as currently defined forOverlay PTC address most of the movement authority needs. Other messagesmay be added or modification to existing messages may be required tosupport QMB as the design progresses.

The core QMB functionality relies on the issuance of exclusive movementauthorities known as PTCEAs 40, 42. PTC manages movement authorities(e.g., track warrants) today using a sequence of four messagesexchanged. FIG. 4 depicts the message sequence for the issuance ofPTCEAs for the four-message exchange model and is described by thefollowing general steps.

-   -   1. (With RVLDS): Message 1 x is triggered and is sent from the        EOT to the HOT of Train1.    -   2. (With RVLDS): Message 1 xa is sent in response from the HOT        to the EOT of Train1.    -   3. Message 1 a is sent to the office and initiates the PTCEA        rollup 50 of Train1.    -   4. Message 1 b is sent to Train1 confirming the PTCEA rollup 50.    -   5. Message 1 c is sent to Train1 and provides the new rolled-up        PTCEA.    -   6. Message 1 d is sent to the office confirming the new        rolled-up PTCEA.    -   7. Message 2 a is sent to Train2 with a PTCEA extension 52.    -   8. Message 2 b is sent to the office confirming the PTCEA        extension 52.

The following considerations and modifications can be made to thegeneral list of steps.

-   -   RVLDS messages are optional and depend on whether RVLDS is        available on a train.    -   The frequency of the above sequence may depend on the distance        between and the speeds of the two trains.    -   Steps 5 and 6, above, could be removed to establish the        two-message exchange model. This is recommended for QMB-equipped        trains in order to reduce unnecessary communications loading.        Messages 1 c and 1 d need to be kept for non-QMB trains.    -   Steps 7 and 8 depend on the proximity of a following train.

FIG. 5 depicts the message sequence for the issuance of PTCEAs for thetwo-message exchange model that is preferred for QMB. This model reducesmessage loading, especially for close-following moves. The two-messageexchange shifts the paradigm of train control in that the onboardsegment makes a change to its authority and then informs the remoteoffice about this change. One further consideration is that QMB isdifferent than the existing mandatory directive (MD) architecture. Also,Message 1 a can update the MD dataset in both the office and locomotive.A train can only reduce its own PTCEA limits, but not increase them,thus making it more restrictive.

Locomotive Onboard Segment. If the present system is implemented withthe original overlay version of ITC-PTC (also known as “O-TTC”), theonboard software is modified to implement functions related to the PTCEAconcepts such as automatic PTCEA rollup 50. Another fundamentalmodification for QMB trains is the ability for PTCEA concepts (e.g.,every train requiring authority conveyed in a movement authority messagein addition to WSMs) to be active in all conventional signaledterritories (e.g., CTC and current of traffic). An example of how thiswould affect the implementation of a PTC system, such as ITC-PTC, isthat the form-based authority required parameter in the track databaseis changed to allow for the acceptance and enforcement of unidirectionalmovement authority data set messages in CTC and GCOR 9.14/9.15 (currentof traffic) territory.

At least the following three classifications of train types areaccommodated where QMB is in operation: QMB, non-QMB train withfunctioning Overlay-PTC (O-PTC), and non-enforcing or non-communicating.Table 2 presents each train type and the corresponding description.

TABLE 2 Train Classifications for QMB Operation QMB train Train withfully operational PTC on board at least its lead locomotive, running QMBonboard software. Backwards compatible and could return to O-PTCoperation (especially as a part of migration path or to accommodatedifferent types of territory). Non-QMB Train with PTC onboard segmentfully operational, train with running onboard software of a versionprior to QMB functioning (e.g., during migration). Overlay-PTC Crew mustmanually roll up PTCEAs, e.g., via existing ITC-PTC messages with arequest type to roll up an existing authority. Non-enforcing Train withonboard segment that has failed en or non- route, or that is notequipped. communicating Burden is on dispatcher and train crew to (NENC)communicate PTCEAs verbally. There is potential train for automated(e.g., synthesized) voice dispatching to reduce the probability of humanerror and workload.

It should be noted that one method of handling non-QMB trains moreefficiently is to add a QMB-equipped locomotive to the lead of anyconsist entering QMB territory. For non-QMB trains, a burden is added tothe train crew to manually roll up the PTCEAs. There is an option tohave the office automatically roll up PTCEAs based on WSMs, but thisrequires always having an unoccupied block behind the non-QMB train.When trains need to follow each other closer than that, manual rollup isrequired.

A rear-of-vehicle location determination system (RVLDS) is an optionaltechnology that can complement QMB operations. The onboard segmentrequires certain software functionality in order to use RVLDS in supportof QMB, including message flow for reporting location (or informationfrom which location can be derived) from the rear of the train to thefront of the train, train pull-apart detection (which can be derivedfrom comparing rear-of-train location to the front-of-train location),and for crew interactions during switching operations when RVLDS can beon a portion of the train that is intentionally separated from the frontportion of the train.

As an alternative to having RVLDS report absolute rear-of-train locationin every report, a portion of the messages sent by RVLDS can reportdistance from the last RVLDS rear-of-train location or distance reportor average rear-of-train speed since last RVLDS report. Thesealternative forms of RVLDS report messages can allow the messages to besmaller in order to consume less radio communications resources (e.g.,throughput or bandwidth). In that case, an application at the front ofthe train converts each alternative RVLDS report in relation to anoccasional absolute location report from RVLDS into reports ofrear-of-train location for use by the QMB onboard.

Wayside Interface Units (WIUs) 25 are used as the single interface withfield devices (track circuits 32 and switches or their associated fieldlogic) under QMB. No modifications to existing WSMs are required whilefield interlocking is retained with conventional signal indication.Instead, the QMB onboard software interprets the WSMs in accordance withTable 3. Note that the onboard interpretation with three circuit states(Clear, Restricting, Stop) provides a capacity benefit that is possibleto achieve without QMB.

TABLE 3 Optional Onboard Interpretation of WSMs While Wayside Logic isActive Onboard Interpretations WSM Signal Non- QMB: Indication OverlayPTC QMB Advance Approach Advance Approach Clear Approach Approach ClearRestricting (e.g., at Restricting Restricting an intermediate) Stop(e.g., at a CP) Stop Stop

Once wayside logic is removed, QMB trains will only experience anAbsolute Stop at locations where absolute signals previously existed,i.e., at OS track circuits 32, and at any other monitored switchlocations. All other track circuits, including those adjacent to an OS,will report Restricting as their most restrictive aspect. The concept of“Approach” and “Advance Approach” signals will no longer be needed.

Optional onboard functionality can be implemented to take advantage ofthe direct locomotive-to-WIU communication path, combined with the PTCEAissued to a train. PTCEAs contain the outcome of the QMB interlockingfunctionality, which CIXL (if implemented) uses to generate commands tothe wayside. CIXL uses the same PTCEA sent to the approaching train bythe QMB office 10. This design allows for an additional switch controloption, where a train can directly command the field based on its PTCEA40, 42 since it contains the same interlocking information that CIXLuses to command the wayside. This functionality can increase the overallsystem reliability, for the exceptional cases when the wayside does notreceive a switch command from the office. The locomotive to WIUcommunication could also be used to allow trains to command switchesduring switching operation. Even where CIXL is not implemented, thissame method can be implemented and applied (when authorized by adispatcher) at any powered switch.

Office Segment. While QMB uses the functional architecture describedherein, the physical office architecture is assumed to be railroadspecific. Various physical architectures are possible with the officesegment and can be determined by the deploying railroad. Therefore, theoffice segment 10 is described in terms of functional architecture, notphysical architecture. In general, the main components of the officesegment include the CAD system 12, QMB office functions 14, and theexisting back-office server (BOS) 16.

No changes are expected to be required to the way in which the CADsystem manages authorities for trains. The CAD system 12 continues toplan movements, issue route requests to field interlockings, handleresponses from the interlockings, and when necessary, issue mandatorydirective authorities to trains (e.g., Track and Time, Enter Main Track(EMT) between signals in CTC territories, Track Warrants (or equivalent)in non-signaled and TWC-ABS territories, Track Permits in current oftraffic (GCOR 9.15) territory, and Authority To Pass signal at Stop(ATP) anywhere absolute signals exist). Similar to how CAD provideselectronic Track Warrants and bidirectional authorities in the form ofCAD-MAs to PTC, it must be modified to also provide CAD-MAs forunidirectional authority in CTC and current of traffic (GCOR 9.14 or9.15) territory. Changes are required for the CAD system 12 to interfacewith the QMB office functions 14 (e.g., for CAD to provide CAD-MAs tothe QMB office). CAD must also be modified to enhance its interface withdispatchers, such as to support the creation and updating of PTCEAs fornon-enforcing or non-communicating (NENC) trains. Track bulletins aregenerally handled independently from QMB-specific functions.

A route that is cancelled or modified by the dispatcher can be acceptedor rejected by the interlocking system. CAD then updates the CAD-MAaccordingly for the affected train. The QMB office 14 then updates thetrain's PTCEA based on any updates to the CAD-MA. For a CAD-MAcancellation, the train's PTCEA will not be totally eliminated if thetrain still occupies any track identified within that PTCEA, since everytrain on main track in QMB territory must have a PTCEA permitting it tobe there. Possible options for CAD-MA cancellation include no furtherPTCEA extensions to the train (if the portion of the route canceled wasnot yet included in the existing PTCEA), truncating its existing PTCEA,or issuing a replacement PTCEA that is shorter.

Functionality may be optionally included for emergency situations, suchas a train entering main track without authorization or when a trainoverrides its authority. In addition to verbal communication, the CADsystem 12 or dispatcher can send out an electronic emergencynotification to all affected trains. The QMB office also providesprevents the issuance of PTCEAs in tracks where trains have overriddentheir authority. The train's onboard segment may immediately warn thecrew and then optionally apply braking and send a response back to theoffice indicating that it has truncated its PTCEA to its predictedstopping location or short of the hazard.

The QMB office functions 14 are additional functions necessary for QMBoperations, beyond those implemented by existing office systems. Thesefunctions include and are not limited to:

-   -   Process movement authorities from the CAD system 12 (CAD-MAs) to        parse them (reduce their limits) when necessary to eliminate        overlap with any other existing PTCEA for another train and        convey the authorities to trains as PTCEAs. Mandatory Directives        (MDs) that don't require parsing just pass through the QMB        office without changes to their contents (payload).    -   Identify and maintain record of each train's type: QMB; non-QMB        (e.g., Overlay PTC); non-enforcing or non-communicating.    -   Perform PTCEA extensions 52 for any train type, based upon PTCEA        rollups 50 for any train type.    -   In a leading-following train pair, relay information to the        following train regarding whether the leading train has        functioning RVLDS.    -   Perform safety-critical functionality to verify that all PTCEAs        are safe and non-overlapping.

The baseline QMB office functionality 14 issues a PTCEA to a train forthe entire length of its CAD-MA when no other train's PTCEA conflicts.However, the QMB office functions 14 can optionally be configured to notnecessarily convey an entire train's dispatcher movement authority tothe train's onboard segment, but rather limit it to a certain distanceand update it as the train moves. For example, if a long route iscreated in the CAD system that extends through several control points,the QMB office functions may send a PTCEA to the train including justthe first five control points. If the chances for modifying a train'sroute are high, this configuration could save unnecessary messagetraffic between the QMB office functions and the onboard segment whenthe dispatcher changes train routes. Conversely, if the chances formodifying a train's route are low, such configuration would causeunnecessary message traffic between the QMB office functions and theonboard segment. A railroad might configure different limits on PTCEAlength on a territory-by-territory basis or may choose not to limitPTCEA length at all.

On its validation by the office, a PTCEA is electronically issued to anenforcing train. A PTCEA may be the original issuance, an extension, ora truncation (e.g., modification). The PTCEA can extend up to the limitof the CAD-MA route if no conflicting moves or PTCEAs are involved.Further, speed restrictions are applied to the train, when necessary, bythe same means already existing in O-PTC. Authorized speed is alsolimited by track database (civil) restrictions, track bulletin data, andWIU status messages for restricting signals. Some types of operation mayrequire a speed restriction in the PTCEA, such as joint authorities.

During a PTCEA rollup 50, a train releases a part of its authority fortrack that it has cleared and sends a report to the office 10. The trainthen recognizes its new rolled-up “From” limit. After the office 10 hasreceived a rollup report and updated the PTCEA database, it can thenextend the PTCEA for another train to operate on the released track. Therollup rate is configurable and may be automatically changed in realtime by the QMB system as conditions change.

The onboard segment includes a safety margin 54 in its PTCEA rollup 50limit calculation, or “From” limit. The safety margin 54 accounts foruncertainties in determining the potential rear-of-train location. Fortrains that do not have functioning rear-of-vehicle locationdetermination, the rear location used by QMB is based on the trainlength calculation and front-of-train location. FIG. 6 illustrates therear-of-train safety margin 54 and the PTCEA 42 for a following train.When QMB uses the estimated consist length because RVLDS is notavailable, the margin 54 added to the train's rear location for QMBpurposes is at least equal to the uncertainty in the train length(accounting for factors including train stretching and erroneous consistdata) plus the uncertainty in determining the location of the front ofthe train. For the case of a train with functioning RVLDS, the margin 54added to the train's rear location for QMB purposes is at least equal tothe RVLDS location uncertainty, plus an allowance for train stretching.The system also allows for the possible need to back up to bunch a heavytrain or similar operation and other considerations which might requireadditional margin at the end of PTCEAs.

When trains on the same route (track) are many miles apart, their PTCEAscan be rolled up infrequently, e.g., once a minute or less often.However, when a train is following another train at a closer spacing,there is a need for the leading train to roll up its PTCEA at a fasterrate so that capacity is not wasted spatially between the leadingtrain's PTCEA “From” limit and its current rear position. A fasterrollup rate does, however, cause additional message traffic loading inthe communication system due to more frequent PTCEA rollups.Consequently, as conditions change, a train's automatic rollup rate ortriggering is adjusted in real time by the QMB system to achieve abalance between avoiding excessive communications loading versusimpacting traffic capacity. The objective is to rollup only as often asnecessary to avoid increasing train separation.

At least three potential methods of triggering rollups 50 are possible:(a) roll up every XX seconds (temporal rollup); (b) roll up every XXfeet (distance-based rollup); or (c) Roll up at designated trackfeatures such as track circuit boundaries and/or track points ofinterest that can be detected by the train and/or identified within thetrack data. If more than one of the above rollup-triggering methods isselected, the onboard segment will roll up at both or all three,whichever comes first, and potentially reset the time or distancecounter at each rollup.

The baseline approach is to implement only a temporal rate of rollupsthat is commanded by the office to each train's onboard segment. Thefirst rollup rate command message from office to onboard segment wouldbe sent during or just after PTC initialization of the locomotive,unless the default rollup rate is to be used initially for that train.The office would send another message to the onboard segment wheneverthe rollup rate needs to change. Other options for determining eachtrain's rollup rate or triggers are available, however, that may or maynot involve the office sending a command to a train's onboard segment.

Each railroad can devise its own office-centric algorithm forsetting/changing each train's rollup rate, because there is no need forevery railroad to use the same algorithm—it will not impactinteroperability. They must all use the same message format, however, tocommand a train to roll up at the desired rate if they wish to beinteroperable with one another and choose an office-centric algorithmfor controlling rollup (temporal) rate.

Rear-of-train rollup locations (“From” limits) received at the office inrollup messages alone provide sufficient information to support anoffice-centric rollup rate management algorithm (RURMA). However,additional or alternative information can be used by the algorithm, atthe preference of the host railroad.

A potential enhancement to this approach, as an example, is for theonboard segment to include its speed in each PTCEA rollup message forthe office to use to improve its prediction of how often rollups will beneeded. Another potential alternative or enhancement is for the onboardsegment to inform the office of when it gets within a specified distanceor time from having to apply braking enforcement with respect to itsPTCEA “To” limit. This would provide indication that the rollup rate mayneed to be increased.

FIG. 7 is a bounce diagram that illustrates the message flow andincludes the following processes: (1) increase PTCEA rollup rate, (2) arepeating message flow, and (3) decrease PTCEA rollup rate. The messageflow diagram is one approach, and others can be considered.

QMB does provide a capacity benefit, which should first be consideredwith respect to common operational practices as well as the capacitygains that can be obtained with conventional track circuits 32. Thecommon operational preference of crews to separate trains by sufficientdistance such that a following train can maintain a fairly constantspeed (rather than having to oscillate between reducing speed for a morerestrictive signal and then increasing speed when the signal clears) canstill be applied under QMB operation. A QMB train following anothertrain knows approximately when/how often and where the train ahead rollsup its PTCEA, since each rollup 50 by the leading train will result inextension 52 of the following train's PTCEA 42. The following train alsosees when each track circuit 32 ahead is cleared by the leading train,based on WSMs received. Consequently, the QMB onboard segment canoptionally provide a pacing cue the crew of a closely following train tokeep sufficient distance from and maintain a steady state speedapproximately equal to that of the train ahead.

QMB obtains a capacity benefit with conventional track circuits 32 andinterpretation of three track circuit states (Clear, Restricted, Stop).However, this capacity benefit is available without QMB. Potential trackcircuit enhancements can facilitate increased capacity beyond thatachievable with conventional track circuits and the three track circuitstates. Two possible track circuit enhancements include a virtual blocktrack circuit (VBTC) and a Next Generation Track Circuit (NGTC).

VBTC refers to a track circuit that can detect and locate an occupancyor rail break to a subsection of the track circuit known as a virtualblock. VBTC can detect a rail break in an occupied block 34 (with somelimitations when more than one train occupies the track circuit). VBTCinterfaces with the onboard segment and the office basically in themanner same as conventional track circuits, using WSMs, withoutnecessarily requiring modifications to the onboard segment or office.

NGTC is a type of track circuit that detects a broken rail within anoccupied block 34 by measuring electrical current on the transmissionend in addition to measuring voltage. The voltages and currents areconverted to Boolean states (e.g., true/false, high/low, one/zero) byusing predetermined threshold values. If the transmission current (“TxCurrent”) in the loop is substantial and is converted to a Boolean stateof one, then the track circuit is clear of broken rails within thatcurrent loop. If the Tx Current is being transmitted and the currentloop is near zero and is converted to a Boolean state of zero, thenthere is a broken rail. By combining the information from thetransmission current and the received signal (“Rx Signal”) based ontransmission from the opposite end, the following states and outcomesare possible as seen in Table 4. This technology was previouslydisclosed in U.S. Patent App. Publ. No. 2018/0327008 (Kindt et al.)

TABLE 4 NGTC WIU Indications Tx Rx NGTC Current Signal Meaning WIUIndication 0 0 Broken rail between Restricted transmission side andshunting axle or in an unoccupied block 0 1 Not normally possible sothis NGTC is inoperable indicates an NGTC failure (Restricted) 1 0Occupancy somewhere in Clear to proceed at block MAS, but other Nobroken rail between conditions need to be transmission side and metincluding the shunting axle leading train having Train can enter at MASRVLDS. Note: In the case that a PTCEA extends through the entire block,but the authorized train has not yet entered the block, this stateindicates a rollout or another anomaly. 1 1 Clear Clear to proceed atMAS

To provide a following train with the most up-to-date informationrequired to achieve minimal headway, the following steps occur:

-   -   During a PTCEA roll up, the (leading) train indicates that it        has operational RVLDS within its rollup message to the office.    -   The office issues a PTCEA extension 52 to the following train        indicating that it can continue at MAS into an occupied block 34        (based on the office's knowledge of operational RVLDS on the        train ahead) and is contingent on the train receiving a valid        WSM that confirms that NGTC is operational in the block.    -   The following train receives the PTCEA from the office and valid        NGTC-based WSM confirming that it can proceed at MAS.

Once the above recommended steps occur, then the following train canenter the occupied block 34 at MAS and maintain MAS within theconstraints of the braking curve and PTCEA limit, as shown in FIG. 8.Once a following train enters the block, it is limited to restrictedspeed (shown by the dashed vertical line) beyond the last reportedrear-of-train location reported by the leading train until the leadingtrain clears the same block and no broken rails are detected.

QMB will leverage the display and enforcement of existing mandatorydirectives. In most cases, a QMB train's PTCEA “To” limit is displayedas a Stop target (red fence) on board. This will be enforced as anabsolute stop target as done today.

When there is a pair of trains in a following move, the leading train's“From” limit is the basis for extending the following train's “To”limit. A safety margin 54 is added onto the train's “From” limit toaccount for uncertainties as previously described. Despite the safetymargins 54, there is still a potential hazard when the leading traindoes not have RVLDS. The following train will incur detrimental reliancebecause it assumes its PTCEA “To” limit, based on the leading train's“From” limit, is without error. Below are the potential onboard displaysolutions for the following train's PTCEA target:

-   -   Invisible target (default): The PTCEA Stop target is not        displayed. First, the track circuit boundary preceding the PTCEA        limit is determined. Then, an RSR from this preceding track        circuit boundary is displayed to the right horizon of the screen        (FIG. 9). Both the RSR and the PTCEA Stop target are enforced.        In the case the PTCEA limit aligns with a track circuit boundary        exactly, then an RSR does not need to be displayed and the “To”        end of the PTCEA limit can be displayed. Furthermore, all Stop        targets (e.g., PTCEA “To” limit, O/S, etc.) at or beyond the        nearest block reporting Not Clear are suppressed. This is done        because if other stop targets are displayed, it could lead the        following train's crew to think that their PTCEA extends up to        the O/S, even though the leading train may be closer.    -   Visible target: If RVLDS is verified to be operational on the        leading train, then the PTCEA Stop target is displayed and        enforced at the “To” end of the PTCEA limit. The PTCEA Stop        target relates to the last reported EOT location of leading        train (with margin) that was used to roll up its PTCEA.

Polling and synchronization are existing ITC-PTC processes that ensurethe critical datasets are the same between the office and each onboardsegment. In QMB, movement authority datasets change frequently duringthe PTCEA rollup and issuance processes. Office segment polling isexpected to remain independent of QMB PTCEA updates in the sense thatPTCEA rollups/extensions and polling messages may occur at any giventime relative to one another.

PTCEAs are similar to track warrants in several aspects and thereforecan use similar PTC messaging. The process for rolling up a trackwarrant in the current ITC PTC system involves the exchange of fourmessages between the office and the train whose track warrant is beingrolled up, as shown in FIG. 10. The current polling and synchronizationprocess accommodates that protocol. Although there are a few situationsin which it is unavoidable, use of this 4-message protocol for rollingup all PTCEAs in QMB would create an unnecessarily excessive load on thePTC radio network, due to the much greater rate of PTCEA rollups thantrack warrant rollups, on average. Consequently, a streamlined,2-message rollup process is used for QMB trains, as shown in FIG. 11.

For QMB trains operating with the 2-message rollup protocol, the onboardsegment automatically initiates the PTCEA rollup process and on doing sowill temporarily have a more recent (rolled up) PTCEA “From” limit thanthe office until the office processes the PTCEA rollup sent by theonboard segment. If the office happens to send an office segment pollmessage to the locomotive during this brief time when it is has adifferent PTCEA “From” limit than the train, QMB must have a way toresolve the difference. There are potentially two differences that QMBmust resolve during polling and synchronization. First, the onboardsegment may have a more recent “From” limit than the office. This can beresolved by the onboard segment such that the onboard segment calculatesthe aggregate CRC (or HMAC) for both the old and new PTCEAs.Consequently, there should not be a CRC mismatch in one of the instancesand this avoids the need for invoking a problematic synchronizationprocess to update the train with the office's older “From” limit. Theonboard segment enforces the PTCEA with the more restrictive “From”limit (i.e., the newer PTCEA). Second, the office may have a more recent“To” limit than the onboard segment. This is expected occasionallybecause message 2 a may have been lost or delayed when first sent. Whenthis happens, there is a CRC mismatch on board and the synchronizationprocess is triggered, resulting in the PTCEA being re-sent. This isalready handled by the current O-PTC polling and synchronizationprocess. Some degree of optimization may be needed to adjust the amountof delay that is acceptable before the onboard segment displaysout-of-sync and requires reduced speed and possible disengagement.

In addition to unidirectional authorities, QMB is also able to handlespecial authority situations, including bidirectional authorities, jointoccupancies, and switching operations. For example, QMB handlesbidirectional authorities that are issued by the dispatcher. Similar tohow PTC handles bidirectional authorities today, the PTCEA for anexclusive bidirectional authority is not rolled up while the train,workers or equipment (TWE) are within bidirectional authority limits.The work authority can be rolled-up or voided once the TWE clears thatauthority segment or is manually rolled up by the crew/gang ordispatcher as needed. For bidirectional operation, where an entirecontrol block (between CPs) can be allotted, “Track and Time” is thetype of bidirectional work authority granted to TWE in CTC territory.“Track Permit” is the type of bidirectional work authority granted underGCOR to TWE in GCOR 9.14/9.15 territory. Currently, when bidirectionalauthority is granted in CTC or 9.15 territory, the CPs at either end ofthe territory are “blocked” (set to absolute stop) to prevent other(unauthorized) TWE from entering the work area. In TWC-ABS territory(not 9.14/9.15 territory), a track warrant is generally used to issuebidirectional authority, using line 4.

A joint authority is a type of bidirectional authority that can beshared among multiple TWE. Under QMB operations for the basic case,joint occupancies are authorized by a dispatcher in a similar manner asdone today. That is, all TWE sharing the joint authority are given theentire bidirectional authority limits in their PTCEA along with aRestricted Speed Restriction. A few examples include: (a) joint trackand time in CTC territory; (b) joint track permit in 9.14/9.15territory; and (c) track warrant (lines 4 and 11 or 12) in ABS-TWCterritory.

At minimum, QMB/PTC keeps all authorized trains withindispatcher-defined bidirectional limits, keeps unauthorized trains out,and enforces (upper) speed limit of restricted speed in a jointbidirectional authority. The crews are responsible for avoidingcollisions within the joint authority, per Restricted Speed rules. Thisis referred to as the “basic case” of QMB joint bidirectionalauthorities.

In the optional advanced case, QMB provides additional protection forjoint occupancy operation by issuing and enforcing an exclusive PTCEA toeach individual TWE within the bidirectional limits. This requiresmonitoring the locations of individual QMB trains (as well as workersand equipment if they are equipped with QMB) and their PTCEAs insidedispatcher-defined bidirectional limits. The concept is described in theexample steps below.

-   -   Step 1: Joint Occupancy Issuance. The dispatcher initiates a        dispatcher-defined joint occupancy for multiple instances of TWE        to work within the same track limits. Note that in some cases,        an exclusive bidirectional authority is issued to the first        train and is later changed to a joint authority later when        another train is ready to enter the limits. The QMB office then        issues exclusive PTCEAs and Authorization to Pass Signal at Stop        (ATP) equivalent to one train at a time, to allow TWE within        limits, as shown in FIG. 12.    -   Step 2: PTC Exclusive Authority Issuance. TWE (person) requests        (via the onboard segment) an authorization to move to a        destination further inside the dispatcher-defined        jointly-occupied limits, as shown in FIG. 13. The QMB office        extends the PTCEA to the extent safe to do so.    -   Step 3: As a rail vehicle moves, the onboard segment enforces        movement based on its granted PTCEA, as shown in FIG. 14.    -   Step 4: Other personnel operating TWE in the jointly occupied        dispatcher-defined limits request PTCEA extensions and operate        simultaneously inside the dispatcher-defined limits, with PTCEAs        managed by the office, as shown in FIG. 15.    -   Step 5: TWE may need to roll up its PTCEA to release a portion        of track when personnel from another TWE requests a PTCEA        extension 52. This is coordinated by the office or the        dispatcher.

The following is an example of the interaction between the rail vehiclesjointly occupying bidirectional limits, as illustrated in FIG. 16.Vehicle C requests an extension of its PTCEA to MP X. The office thensends a request to Train A (the one currently holding a PTCEA over partor all of the requested extension area) to roll up its PTCEA to thenecessary location. Train A can respond indicating: (a) The existingonboard PTCEA has been rolled up; or (b) The existing onboard PTCEA hasbeen rolled up only up to MP Y; or (c) The PTCEA cannot be rolled up atthat time. Only after Train A responds with option (a) or (b) can theoffice roll up Train A's PTCEA in the office database; and lastly,extend Vehicle C's PTCEA. The crews can communicate among themselves toresolve conflicts (e.g., using voice radio). If a conflict cannot beresolved between crews, then the dispatcher can help resolve it.

It should be noted that TWE are allowed to move bi-directionally withintheir respective PTCEAs, as needed, under bidirectional authority. Anytype of TWE (hi-rail, service units, regular trains, gangs) withauthority to do so can operate within bidirectional limits. The choiceof bidirectional limit locations is not necessarily restricted (by PTC)to any specific physical constraints, such as a track circuit boundaryor CP. Restrictions can be added, however, to only allow definition oflimits at human actionable or identifiable locations. Once thedispatcher issues bidirectional authorities for joint occupancy, theentire operation of trains might be completed without burden to thedispatcher if all TWE involved are QMB-capable. If there is mixedtraffic with non-QMB vehicles, and the burden for the crew anddispatcher becomes significant, it might be preferred to use the basiccase mode of QMB operation. If trains change length, decouple, etc., thecrew or the dispatcher must update the PTC consist data. As in currentrailroad operations, broken rail protection within joint bidirectionallimits is limited due to the high instance of track circuits beingjointly occupied; this can be improved where NGTC is implemented. Thefallback mode of operation for the advanced case (e.g., in case offailure or an incapable onboard segment) is the basic case.

There is a corner case for helper/rescue locomotives or intentionalsplitting or combining of trains. Safety margins required on PTCEAs donot allow two trains with exclusive PTCEAs to come close enough togetherto couple. In this case, both trains should be given basic jointbidirectional authorities for coupling. The joint bidirectionalauthorities are issued when trains are close and stopped (or below TBDmph) to allow combining/merging of their trains. After physical couplingof the two trains and then taking one train's onboard segment out of theActive state, the two trains' joint bidirectional PTCEAs are replaced bythe dispatcher with a single, exclusive PTCEA (typically unidirectional)assigned to the train ID of the train whose onboard segment remains inthe Active state. Only that one trains ID remains in use. Similarly, abidirectional authority is used when a train needs to split into twotrains. This stops rollups and allows sufficient limits in the PTCEA forthe two parts of the train to become sufficiently separated to allow themargin required for creation of two exclusive PTCEAs. A new ID isrequired from the dispatcher/office for the new train (the segment thatdoes not include the original QMB controlling locomotive).Alternatively, a special mode could be created for the joining orsplitting of trains.

QMB supports switching operations in which cars need to be picked up orset out. Switching operations are notably different than normalunidirectional QMB operations as the trains can move in both directionswithout bidirectional authority and with changing consist lengths. Thebasic approach for switching operations involves QMB providing a methodfor operators to set limits to keep the PTCEAs of other trains fromencroaching upon the planned switching zone. Typically, the dispatcheror train crew enters limits for switching. The QMB office uses these“Switching Limits” for the train that is to perform the switchingoperations, as follows. The PTCEA of the train performing switching isconstrained to not be less than the Switching Limits (i.e., theswitching train's PTCEA is not rolled up to any point within theswitching limits during the switching operations). The train crewperforming the switching operations uses the existing PTC RestrictedState (the switching PTCEA's limits are not enforced by the trainperforming the switching, but it is under a Restricted SpeedRestriction). The QMB office creates PTCEAs for other trains as neededthat do not conflict with the switching train's PTCEA, as with any otherPTCEA. This provides protection such that nearby trains do not enter thelimits of the switching train's PTCEA. When switching operation is done,the dispatcher or train crew removes the switching limits and theswitching train's PTCEA is now able to be rolled up without switchingconstraints.

An optional advanced switching feature is possible in which the trainperforming switching, or at least its lead locomotive, are enforced toremain within the switching limits. All else would remain the same asdescribed above for the basic switching approach.

If at the time the dispatcher requests switching limits, the switchingtrain's PTCEA does not include those entire limits, the office attemptsto automatically extend the train's PTCEA. This may also require firstrolling up the PTCEA of another train if it includes any track withinthe desired switching limits.

A centralized location that provides geographic boundaries where QMBoperation is enabled or disabled (i.e., defining the limits of QMBterritory) is necessary. It is recommended that the CAD systemunderstands the geographic areas to be defined as QMB territory,especially because CAD-MAs will need to be generated for allunidirectional authorities where QMB is operational.

All trains require a PTCEA, which is a type of form-based authority(particularly from PTC's perspective), in QMB territory. There is aparameter in the ITC PTC track database that is set to require amovement authority message in QMB territory. For QMB trains, anothermechanism is used in addition to setting the form-based authorityrequired parameter in the track data. If QMB territory were definedsolely by the formed-based authority required parameter, then QMBfunctionality could unintentionally be enabled in territories that useform-based authority required (e.g., TWC) without any option to disableQMB functionality.

Thus, QMB functionality is enabled in CTC territory when the form-basedauthority required parameter is set in the track data, and aQMB-specific authority type is given in the ITC-PTC movement authority(PTCEA) message. The office determines the train type duringinitialization and then sends the proper authority type to each traineach time a new PTCEA is needed. Potential authority types for QMBtrains include: (a) PTCEA without RVLDS on leading train/no leadingtrain; and (b) PTCEA with RVLDS on leading train. The above methodavoids the need to create and maintain different versions of track datafor QMB versus O-PTC trains. However, an acceptable alternative approachis to designate where QMB is enabled in track data.

Within QMB territory, there are processes for enabling and disabling QMBoperations, e.g., for supporting major system maintenance activities.These processes involve multiple steps and are not expected to be donefrequently. Table 5 provides a process for enabling QMB operations andTable 6 provides a process for disabling QMB operations. An individualrailroad has the discretion to enable or disable QMB operations whilenoting the potential burden on the dispatcher and/or train crews withmixed mode operations. The percentage of available QMB trains (e.g., 25,50 or 75 percent) can be a factor in choosing when to enable QMBoperations.

TABLE 5 Enabling QMB Operations Step Description Outcome 0 A person withthe proper authority Authority is provided to determines that QMB modeshould be continue with the steps enabled. below. 1 Set form-basedauthority required for Track data is changed. intended QMB territories.This will likely be done by the railroad's track data management team. 2Use normal processes for updating Track data is track data for alltrains, synchronized between the office and onboard segments. 3a Officestarts sending PTCEA messages QMB mode begins for to non-QMB trainswith: non-QMB trains in the Crew Action Required = RR- given territory.specific Authority Type = “Track warrant/track authority” Note: Crewwill need to be informed they need to manually roll up their PTCEA at anappropriate rate. 3b Office starts sending PTCEA messages QMB modebegins for to QMB trains with: QMB trains in the given Crew ActionRequired = “No crew territory. action required” (recommended) AuthorityType = “PTCEA [. . . ]”

TABLE 6 Disabling QMB Operations Step Description Outcome 0 A personwith the proper authority Authority is provided to determines that QMBmode should be continue with the steps disabled. below. 1 Returnform-based authority required to Track data is changed. its originalvalue based on the original territory. 2 Use normal processes forupdating track Track data is data for all trains, synchronized betweenthe office and onboard segments. 3a Office discontinues sending PTCEAQMB mode is disabled messages to non-QMB trains for for non-QMB trainsin unidirectional authorities in CTC and the given territory. 9.14/9.15territory. When/where form-based authorities are required in the absenceof QMB (e.g., in track warrant territory and for bidirectionalauthorities, ATP and in the messages. EMT), legacy authority types areused 3b Office discontinues sending PTCEA QMB mode is disabled messagesto QMB trains for unidi- for QMB trains in the rectional authorities inCTC and 9.14/ given territory. 9.15 territory. When/where form-basedauthorities are required in the absence of QMB (e.g., in track warrantterritory and for bidirectional authorities, ATP and EMT), legacyauthority types are used in the messages.

It should be noted that the steps for either process (enabling ordisabling QMB) may not happen simultaneously for all trains. Some trainswill be in QMB mode while others may not until all have applied therevised track data. The office keeps record of when each traintransitions to using the new track data so that it can send theappropriate authority type in any PTCEA message sent to that train. Afollowing train without a PTCEA may encroach upon a leading train'sPTCEA, if its crew is not adhering to non-QMB operating rules.

The deployment of QMB may be gradual. It is possible that at thebeginning of operation of QMB in a territory, a significant percentageof trains in operation on that territory will not be upgraded with QMBsoftware on board, either because of the gradual upgrade of onboardsoftware (particularly if the fleet operating in that territory is notcaptive), or because of operation of trains from foreign railroads thathave not yet migrated to QMB. Retaining wayside signals allows moreefficient handling of non-QMB trains during the transition period.

It is assumed that QMB train control will be deployed in select areasalready established as Overlay PTC territory. Consequently, there willbe operational scenarios in which trains will transition into and out ofQMB territory. Transitions will utilize existing processes, such astransitioning into and out of TWC territory.

While in QMB territory, a QMB train may at any time become anon-enforcing or non-communicating (NENC). A NENC train may have afailed onboard segment, an onboard segment that is communicating but isnot in an active state, an onboard that is not communicating, or may beunequipped with any form of PTC.

There are existing processes today for handling trains that are NENC.Generally, these are onboard-centric processes, and the office segmentdoes not act upon that information. For QMB operation, there needs to bean indication of a NENC train in the office segment. This helps todirect how the PTCEA is provided to the train. If enforcing (i.e.,active) and communicating, then the PTCEA is electronically issued tothe QMB train. If non-enforcing or non-communicating, then the PTCEA issent to the CAD system and the dispatcher verbally issues the PTCEA tothe train crew.

A train is determined to be non-enforcing by the office upon receiving amessage that is different than the active state. A train is once againenforcing upon receiving a message that it is in an active state.

A train is determined to be non-communicating by the office if thattrain does not respond for a specified number of consecutive messages.To restore a non-communicating train back to communicating, the officeshould listen for (or subscribe to) any message that the onboard of suchtrain sends. Note that it is unknown to the office whether the train isenforcing or non-enforcing while it is non-communicating.

QMB has features that can provide additional protection (as compared torelying on conventional CTC systems) and potentially reduce the burdenon the dispatcher to handle loss of shunt scenarios as described below.

If a train fails to shunt a track circuit, a conventional signalingsystem may release a route to be issued to another train, which is aconcern when operating light trains or on tracks where conditionsfacilitate loss of shunt. In QMB, the office retains a train's PTCEAuntil it has received a rollup message from the train even when thetrack circuit where the train is located reports unoccupied. FIG. 17illustrates a potential loss-of-shunt scenario, where Train1 that isoperating and maintains an active PTCEA but fails to shunt, and theoffice prevents a PTCEA from being granted to Train2.

When train cars pull apart, the momentum of the separating cars might bein the same direction or in the opposite direction of the originalconsist (e.g., a slow train on a steep uphill grade). Either way, theseparation of the air hoses between cars should trigger the air brakesto go into an emergency application (as long as the air hose [brakepipe] contains no blockages or closed angle cocks) in order to slow downand ultimately stop the separated cars (for as long as sufficientreservoir air pressure remains). The degree of QMB protection thendepends on whether there is rear-of-vehicle location available. In anycase, there is no less protection in QMB territory than exists todaywithout QMB. But additional protection exists under QMB operation whenthe train pulling apart has rear-of-vehicle location determinationfunctionality.

If there is rear-of-vehicle location determination, there are threeprotective measures with regard to a train separation (pull apart).First, the onboard segment will detect the train has pulled apart whenthe reported or derived rear-of-train location falls behindfront-of-train location plus the estimated train length plus margin 54.The onboard segment alerts the crew and other trains in the area thatthe train has pulled apart. This is beneficial because: (a) informationis quickly provided regarding the cause of the emergency application; or(b) there could be cases in which an emergency brake application doesnot occur (e.g., brake pipe is blocked). Once detected, the onboardsegment and/or head-of-train device immediately warns the crew, and acommand can be sent over the head-of-train to end-of-train radio link toautomatically apply emergency braking at the end of the train.

Second, any subsequent rollup reports are based on the rear-of-vehiclelocation determination system with safety margin such that the rolled upPTCEA includes the track occupied by the separated cars.

Third, WSMs from the track circuit occupied by the pulled apart carsresult in an RSR for the occupied track circuit(s). However, a trackcircuit does not provide protection if the following train has alreadyentered the track circuit before the separating cars leave the trackcircuit, or if the separated cars do not shunt the track circuit.

The following is an example case for pull-apart protection (FIG. 18)with rear-of-vehicle location determination functionality. OS isreporting clear. The rear-of-vehicle location determination system isreporting its location on the main track (or alternative information[e.g., distance from last reported location] from an application at thefront of the train can derive rear-of-train location). The estimatedtrain length plus margin is shorter than what is indicated byrear-of-vehicle location determination system. Pull-apart is detected byTrain1 and a message is sent to the office. Train1 PTCEA can be rolledup, but not beyond Train1's reported rear-of-vehicle locationdetermination system. Train2 PTCEA can then be extended, but not beyondTrain1's reported rear-of-vehicle location determination system.

For an undetected pull-apart without rear-of-vehicle locationdetermination functionality, any rollup reports after a pull-apart eventindicate an erroneous rear-of-train location since the PTCEA rollup isbased on an estimated train length that is assumed to be intact. Thiserror grows in time as there becomes a greater distance between theseparating cars and the location cited in the restricted rollup report.

Protective measures for QMB trains that pull apart and do not haverear-of-vehicle location determination system reporting are similar totoday's operation: (a) an emergency brake application should occur(assuming brake pipe is not blocked), but no information is available asto the cause of the emergency application; and (b) WSMs from the trackcircuit occupied by the pulled apart cars result in an RSR for theoccupied track circuit. However, as with legacy (non-QMB) operations, atrack circuit does not provide protection if the separated cars do notshunt the track circuit or a following train enters the track circuitbefore the separated cars enter it.

It is possible for a train to clear main track onto a siding while itsPTCEA continues to overlap the OS. This causes a discrepancy betweenfield indications (OS indicates Clear) and the inability to extend thePTCEA for the following train. FIG. 19 depicts the following situationand becomes increasingly more likely based on the length of the safetymargin. The goal of handling margin overlap at the O/S is to avoiddispatcher involvement and to minimize onboard complexity. For example,these goals can be met by the following process. The CAD issues a CAD-MAfor Train2 to pass through the clear O/S. However, the office cannotextend Train2's PTCEA since there is PTCEA overlap due to Train1 marginoverlap. The office sends an electronic prompt to Train1, or thedispatcher contacts Train1, to roll up its PTCEA if it safe to do so. IfTrain1 rolls up its PTCEA, this will clear the issue. If Train1's crewresponds with an indication to wait, then the office waits for furthercrew response. If there is no response after TBC seconds, the officesends another request to Train1's crew. If Train1's crew indicates thatthey cannot confirm their train is clear of the O/S, then the officesends a message to Train2 that provides the identity of Train1 anddirects Train2 to verify that Train1 is clear. Train2's crew informsTrain1's crew (via voice radio) if their train is clear and its PTCEAshould be rolled up or if it needs to be moved to clear the route.

The above disclosure sets forth a number of embodiments of the presentinvention described in detail with respect to the accompanying drawings.Those skilled in this art will appreciate that various changes,modifications, other structural arrangements, and other embodimentscould be practiced under the teachings of the present invention withoutdeparting from the scope of this invention as set forth in the followingclaims.

We claim:
 1. A method for increasing the level of protection provided by a communication-based train control system against collisions among a plurality of trains along a track divided into a series of fixed-block track circuits, said method comprising: parsing the route for each train into exclusive movement authorities; issuing and subsequently updating a movement authority to each train, thereby granting exclusive authority for each train to move within a movement authority; constraining the operation of each train to proceed along the track within its movement authority; automatically rolling up the movement authority to release the portion of the movement authority behind the train with a safety margin to allow for any uncertainty in the rear-of-train location as the train proceeds along the track; extending the movement authority of a potential subsequent train, allowing it to occupy the released portion of the movement authority of the prior train; detecting the existence of occupancy by any rail vehicle in each track circuit by applying and detecting an electrical signal to the rails; communicating the state of existence of occupancy by any rail vehicle in each track circuit to the trains; further constraining the operation of each train to protect against a detected unexpected occupancy within the movement authority of each train; detecting the existence of broken rail in each track circuit by applying and detecting an electrical signal to the rails; communicating the state of existence of broken rail in each track circuit to the trains; and further constraining the operation of each train to protect against a detected broken rail within the movement authority of each train.
 2. The method of claim 1 further comprising enabling a following train to proceed at up to maximum authorized speed into an occupied track circuit block, if the track circuit has the ability to detect a broken rail within an occupied block, upon receiving information that: (a) no broken rails have been detected in the occupied track circuit block between the entry part of the track circuit block in the direction of travel and the rear-of-train location of the leading train; and (b) the leading train that is occupying that track circuit block has a functioning rear-of-train location determination or train integrity determination system.
 3. The method of claim 1 wherein the step of rolling up of movement authorities is repeated over time at a frequency based at least in part on at least one of: (a) the distance between the subsequent train and the rear of the leading train; (b) elapsed time; (c) elapsed distance; and (d) the train location relative to predetermined points along the track.
 4. The method of claim 1 wherein each movement authority rollup location is based on a rear-of-train location determination system that reports absolute rear-of-train location to the front of the train.
 5. The method of claim 4 wherein a movement authority rollup location is determined at least in part from the reported distance traveled by the rear of the train since the rear-of-train location was last reported.
 6. The method of claim 4 wherein a movement authority rollup location is determined at least in part from the reported average rear-of-train speed since the rear-of-train location was last reported.
 7. The method of claim 2 wherein an onboard system on each train applies a restriction when an occupancy is detected within a block by the track circuit for that block and the occupancy is not expected because the train's exclusive electronic movement authority extends through the entire block.
 8. The method of claim 2 wherein a speed restriction is applied in areas with a potential rail vehicle rollout, comprising: providing the onboard track database having information regarding whether there is a derail or rollout detector installed at each switch; the onboard system checking the track database in advance of the predicted braking distance ahead of each switch in a block with an occupancy ahead, and if there is not a derail or detector installed at the switch, the onboard displaying and enforcing a speed restriction at that switch rather than allowing operation at maximum authorized speed; if the train enters the block before the occupancy ahead clears the block, the onboard system continuing to enforce a speed restriction at each hand-throw switch ahead in that block that lacks a derail or rollout detector.
 9. The method of claim 2 wherein a broken rail location is estimated by identifying the rear-of-train position at the time when the track circuit detects the rail break.
 10. The method of claim 1 wherein the system sets the boundary between parsed movement authorities for joint occupants of a bidirectional movement authority based on location destinations requested by a joint occupant.
 11. The method of claim 1 wherein the boundary between parsed movement authorities for joint occupants of a bidirectional movement authority is automatically set based on at least one of: (a) updated reports of location; (b) train speeds; and (c) braking distance from at least one of the joint occupants.
 12. The method of claim 1, wherein movement authorities are provided to each train in a format compatible with the train's level of onboard system functionality and interface protocol as known by the office.
 13. The method of claim 1, where the rate of automatic movement authority rollup by each train is assigned by an off-board system based on changing conditions.
 14. A method for increasing the level of protection provided by a communication-based train control system against collisions among of a plurality of trains along a track divided into a series of fixed-block track circuits, including a remote office communicating via a communications network with the trains, each train having an onboard system operating the train in accordance with movement authority limits received from the office via the communications network, said method comprising: parsing the route for each train into exclusive movement authorities by the office; issuing and subsequently updating a movement authority from the office to each train, thereby granting exclusive authority for each train to move within a movement authority; constraining the operation of each train by its onboard system to proceed along the track within its movement authority; communicating from each train's onboard system to the office via the communications network to automatically roll up the movement authority for each train, releasing the portion of the movement authority behind the train with a safety margin to allow for any uncertainty in the rear-of-train location as the train proceeds along the track; extending by the office the movement authority of a potential subsequent train, allowing it to occupy the released portion of the movement authority of the prior leading train; detecting the existence of occupancy by any rail vehicle in each track circuit by applying and detecting an electrical signal to the rails; communicating the state of the existence of occupancy by any rail vehicle in each track circuit track circuit to the trains; further constraining the operation of each train by its onboard system to protect against a detected unexpected occupancy within the movement authority of each train; detecting the existence of broken rail in each track circuit by applying and detecting an electrical signal to the rails; communicating the state of the existence of broken rail in each track circuit track circuit to the trains; and further constraining the operation of each train by its onboard system to protect against a detected broken rail within the movement authority of each train. 